Optical electronic device including enhanced global shutter pixel array and related methods

ABSTRACT

An optical electronic device may include a plurality of different optical sources, and a global shutter sensor including an array of global shutter pixels, with each global shutter pixel including a plurality of storage elements. A controller may be coupled to the plurality of optical sources and the global shutter sensor and configured to cause a first optical source to illuminate and a first storage element in each global shutter pixel to store optical data during a first integration period, cause a second optical source to illuminate and a second storage element in each global shutter pixel to store optical data during a second integration period, and output the stored optical data from the first and second storage elements of the global shutter pixels after the first and second integration periods.

TECHNICAL FIELD

The present invention relates to the field of electronic devices and,more particularly, to optical electronic devices and related methods.

BACKGROUND

Image sensors are used for a wide variety of applications such asdigital still cameras, machine vision, automotive and gaming, etc. Most2D image sensors have a readout block which is shared among multiplepixels (typically one column's worth). Hence it is not possible to readout multiple rows at a time and so the rows are read out in a sequentialmanner. As each pixel typically collects light for the same amount oftime, the rows of the sensor are sequentially reset. (The time between apixel's reset and a pixel's readout is its exposure, also known asintegration time). If an object (or sensor) is moving during thereadout, there will be artifacts due the sequential nature of the resetand readout. This is called rolling blade shutter artifacts, as they aresimilar to silver-halide film sensors and the mechanical shutter bladesand their associated artifacts.

As a result of such artifacts, a different pixel design is sometimesemployed in digital image sensors, namely “global shutter pixels”. Inthese types of pixels, there is a storage element inside the pixel. In atypical configuration, all pixels on the sensor are simultaneouslyreset, simultaneously exposed and then the signal information issimultaneously transferred to each pixels' respective storage. Thestorage pixels are then read out, typically row sequential. As all thepixels are exposed at the same time, there is no rolling blade shutterartifacts.

While avoiding rolling shutter blade artifacts is advantageous, furtherenhancements to global shutter pixel configurations may be desirable forcertain applications.

SUMMARY

An optical electronic device may include a plurality of differentoptical sources, and a global shutter sensor including an array ofglobal shutter pixels, with each global shutter pixel including aplurality of storage elements. Furthermore, a controller may be coupledto the plurality of optical sources and the global shutter sensor andconfigured to cause a first one of the optical sources to illuminate anda first one of the storage elements in each global shutter pixel tostore optical data during a first integration period, cause a second oneof the optical sources to illuminate and a second one of the storageelements in each global shutter pixel to store optical data during asecond integration period, and output the stored optical data from thefirst and second storage elements of the global shutter pixels after thefirst and second integration periods.

In accordance with one example embodiment, the plurality of opticalsources may be spaced apart from one another. Additionally, each of theoptical sources may be configured to emit light at different respectivewavelengths. For example, the different wavelengths may be in variousranges such as 200 nm to 400 nm, 400 nm to 700 nm, 700 nm to 1000 nm,etc.

The global shutter sensor may further include a plurality ofanalog-to-digital converters (ADCs) coupled to the array of globalshutter pixels, and the controller may read the stored optical data bycausing the ADCs to convert the optical data to digital optical data.Moreover, the global shutter sensor may further include a multiplexercoupled to the ADCs and configured to multiplex the digital optical datafrom the ADCs as an output of the global shutter sensor. Furthermore,the global sensor pixels may be arranged in rows and columns in thearray, each column of the array may include a plurality of bit lines,and the plurality of ADCs may comprise a respective ADC for each of thebit lines. By way of example, the storage elements may comprisecapacitors.

Additionally, the controller may be further configured to cause a thirdone of the optical sources to illuminate and a third one of the storageelements in each global shutter pixel to store optical data during athird integration period, and to output the stored optical data from thefirst, second, and third storage elements of the global shutter pixelsafter the first, second, and third integration periods. Further, thecontroller may be configured to cause third and fourth storage elementsfrom among the plurality of storage elements to respectively store resetsignals associated with the first and second integration periods, and toremove respective reset noise from the optical data stored in the firstand second storage elements based upon the reset signals stored in thethird and fourth storage elements.

A related image sensor, such as the one described briefly above, andoptical imaging method are also provide. The method may include causinga first optical source from among a plurality of different opticalsources to illuminate a first one of the storage elements in each globalshutter pixel to store optical data during a first integration period,causing a second one of the optical sources to illuminate and a secondone of the storage elements in each global shutter pixel to storeoptical data during a second integration period, and outputting thestored optical data from the first and second storage elements of theglobal shutter pixels after the first and second integration periods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic block diagram of an optical electronic systemincluding a global shutter pixel sensor in accordance with an exampleembodiment.

FIG. 2 is a schematic diagram of an example pixel circuit which may beused with the global shutter pixel sensor of the system of FIG. 1.

FIG. 3 is a timing diagram for the system of FIG. 1.

FIG. 4 is a schematic block diagram of another example global shuttersensor arrangement which may be used with the system of FIG. 1.

FIG. 5 is a schematic diagram of another example pixel circuit which maybe used with the global shutter pixel sensor of the system of FIG. 1with a single output line.

FIG. 6 is a timing diagram similar to that of FIG. 3 but for the singlepixel output configuration of FIG. 5.

FIG. 7 is a schematic block diagram of another example of an opticalelectronic system similar to that of FIG. 1 but with one output perpixel and internal line storage.

FIG. 8 is a schematic diagram of another example pixel circuit includingthree parallel storage elements.

FIG. 9 is a schematic block diagram of another example of an opticalelectronic system including the pixel circuit of FIG. 8.

FIG. 10 is a timing diagram for the system of FIG. 9.

FIG. 11 is a schematic diagram of another example pixel circuitincluding four storage elements which may used to provide reset noisereduction.

FIG. 12 is a timing diagram associated with the pixel circuit of FIG.11.

FIG. 13 is a schematic diagram of another example pixel circuitproviding reset noise reduction.

FIG. 14 is a timing diagram associated with the pixel circuit of FIG.13.

FIG. 15 is a flow diagram illustrating method aspects associated withthe system of FIG. 1.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring initially to FIGS. 1-3, an optical electronic system 30illustratively includes an optical source module 31, a global shutterpixel sensor 32 and associated control logic 33, and a processor 34 isfirst described. Generally speaking, the system 30 advantageously allowsfor high-resolution images with different illumination to be acquired ina relatively short amount of time to help eliminate motion artefacts.More particularly, pixels 35 in the global shutter sensor 32 include atleast two storage elements (here capacitors CST1 and CST2) per pixel, sothat the illumination (e.g., an LED of one particular wavelength) isilluminated for a first integration period and then stored inside thepixel, and a second illumination source (e.g., and LED of a differentwavelength) is illuminated for a second integration period and thenstored, after which the whole array is read out. The sensor 32 furtherillustratively includes voltage/current reference circuitry 36 and YDECcircuitry 37.

An example pixel 35 which may be used with the system 30 is shown inFIG. 2. More particularly, this configuration is a voltage-domain globalshutter pixel with two parallel storage elements CST1, CST2, althoughother voltage domain global shutter configurations, such as with twosequential storage elements, may also be used in some embodiments.

In the implementation illustrated in FIG. 1, two LEDs L1, L2 areprovided, each of which is configured to emit light of a differentwavelength. For example, the LEDs L1, L2 may emit light in the visiblerange (400 nm to 700 nm), or in near the IR (700 nm-1000 nm) or near UV(200 nm-400 nm) ranges. The brightness of the LEDs L1, L2 may beadjustable when they are on. The optical source module 31 illustrativelyincludes respective amplifiers 41, 42 for driving the LEDs L1, L2, andthe amplifiers 41, 42 receive respective independent control signalsLED1, LED2 from the control logic 33 to turn on and off each LED. In theillustrated example, brightness is controlled by a signal (voltage orcurrent) output from a digital to analog converter (DAC) 43, and thebrightness of each LED L1, L2, may be independently controlled ifdesired. The photons emitted from each LED L1, L2 may optionally befocused or collimated using an optical element to project a pattern ontoa target, and the reflected photons may be focused onto an imagerincluding the global shutter pixels 35.

As noted above, an advantage of global shutter pixels with dual storagecapability is that this allows two images to be acquired in shortsuccession, shorter than the readout period of the image. In the presentexample, each pixel 35 has two independent output signals OUT1, OUT2,one for each of the capacitive storage elements CST1, CST2 which areconnected to a line “Vx” (aka, “bitline”) which is common to all thepixels in that column. Hence, there are two bitlines VxA and VxB percolumn. Each individual bitline Vx may be connected to an individualreadout (e.g., analog-to-digital converter (ADC) 44), hence there aretwo ADCs for each column, and so the two output signals OUT1, OUT2 fromeach pixel 35 are able to be read out substantially at the same time.The pixel 35 further illustratively includes a photodiode capacitor Cpd,a sense node capacitor Csn, source follower transistors SP#1-SF#3,read/sample switching transistors T1-T4, and reset transistor RT.

The system 30 illustratively includes two outputs OUT1, OUT2 per pixel35, and the two ADCs' (or other readout devices) 44 for each column areadjacent. This implies that the pitch of the ADCs' are half that of thepixel. Depending on the pixel size and process technology, this may notbe practical, hence an alternative arrangement for a global shuttersensor 132 is shown in FIG. 4. Here the ADCs 144 are split, half are onthe top of the array of pixels 135 and half are on the bottom. In thisimplementation, the lines VxA may use adjacent ADCs 144 (e.g., bottom),and the lines VxB may use the adjacent ADCs on the other side of thearray (e.g., top). Another approach is to have even number columns useone side of the array and the odd number columns use the other side,i.e., lines VxA1, Vx81, VxA3, VxB3 etc. use the ADCs 144 on the bottomof the array and lines VxA2, VxB2, VxA4, VxB4, etc. use the ADCs on thetop of the array.

Once each row of signals have been read/converted into digital form,they are multiplexed via a multiplexer X-MUX onto a common output bus(or possibly two output busses, one for data from the ADCs 44 for thelines VxA and one for data from the ADCs for the lines VxB). The outputfrom the sensor 32 is optionally passed to the processing engine 34. Forexample, the processed signal for pixel #N may be calculated from thesignal output from the sensor for each of the exposures, for pixel #N,as follows:PROCESSED(N)=OUT1(N)−OUT2(N).  (1)Outputting processing for a scaled difference may be as follows:PROCESSED(N)=A*OUT1(N)−S*OUT2(N).  (2)Furthermore, output processing for a 3*2 filter configuration would beas follows:PROCESSED(N)=A*OUT1(N−1)+B*OUT1(N)+C*OUT1(N+1)+D*OUT2(N−1)+E*OUT2(N)+F*OUT2(N+1).  (3)Other suitable output processing approaches may also be used.

A timing diagram 45 for the LEDs and two storage global shutterconfiguration system 30 with two outputs is shown in FIG. 3. The framestarts with all photodiodes L1, L2 being reset. This is achieved bytaking the signals RST_GS and TG_GS high (_GS indicates global shutter,i.e., all pixels and all rows for each of the RST and TG signals). Assoon as the TG pulse is low, the pixel 35 is now integrating andsensitive to light, and so the first LED L1 is pulsed on and its lightreflected from target object is detected by the pixels. At the end ofthe determined integration period, the TG pulse is used to transfer thephoto-generated charge into the sense node and preferably a transistorBias for the source follower is enabled and signal SAMPLE1 goes high sothe signal from output of the sense-node source follower SF#1 is storedon the first sample/hold capacitor. After the signal has been stored,the signal SAMPLE1 goes low to turn off the transistor T1 whichdisconnects the storage element CST1 from the source follower. Thetransistor Bias may be turned off to save power, it may stay fully on toenable faster response, or it may be set to a lower power mode for atrade-off between speed and power consumption, depending on the givenimplementation.

The photodiode PD is reset by again taking both the signals RST and TGhigh and then low, but this time the second LED L2 is commanded to turnon and after a predetermined time, the signal TG pulse transfers thecharge to the sense node. This time, the signal SAMPLE2 goes high tostore the signal from the sense-node source follower's SF#1 output ontothe second sample/hold capacitor CST2 in the pixel. After the secondsignal has been stored, the signal SAMPLE2 goes low to isolate thesecond sample/hold signal, and the bias signal may optionally go low toturn off the sense-node source follower transistor and save power. In aglobal shutter pixel arrangement, all of the pixels 35 may be reset andintegrating at substantially the same time. Now the images from bothLEDs L1, L2 are stored in each pixel, and they may be read out in arow-sequential manner. Once all (or a pre-determined) number of rowshave been read out, this cycle may be repeated for further images.

In the system 30, the pitch of the ADCs are ½ that of the pixel. Thatis, if the pixel is 4 μm×4 μm then the ADC may be maximum 2 μm wide tohave the ADCs 44 for each readout adjacent. Depending on the processtechnology used for implementing the system 30, this may be impractical.As noted above, another arrangement is provided with the sensor 132 orFIG. 4, where there are ADCs 144 at both the top and bottom of thesensor. Hence the pitch of the ADC 144 need only be the same as thepitch of the pixel 135. However, a tradeoff with this approach is thatmore space may be required on the sensor 32, potentially resulting in alarger and more expensive sensor.

Referring again to FIG. 3, it typically takes 1 μs to 5 μs to reset thepixel, 1 μs to 10 μs to expose, and a further 1 μs to 5 μs to read thecharge on the photodiode PD, convert this to a voltage on the sense nodecapacitor Csn, and then store on the sample/hold capacitor CST1 or CST2.Hence the time for each LED L1, L2 exposure is a minimum 1 μs+1 μs+1μs=3 μs to a maximum 5 μs 10 μs 5 μs=20 μs. Using the worst case(maximum) value of 20 μs for each LED, then both images can be acquiredinside 40 μs, with only 20 μs separating them (that is, no pixel readoutis required). By way of contrast, in typical global shutterconfiguration there would be approximately 10 ms of time between twosuccessive exposures because of the requisite readout therebetween.Hence, the system 300 may advantageously provide approximately 500×faster exposure between successive exposures.

By way of comparison, consider an example for a typical global shuttersensor which has a horizontal field of view of 50° and the object is 10cm away from the sensor. For a field of view calculation:

$\begin{matrix}{{{HFOV}_{mm} = {{2*{\tan( \frac{50{^\circ}}{2} )}*10\mspace{14mu}{cm}} = {9.3\mspace{14mu}{cm}}}},} & (4)\end{matrix}$if the object is travelling at 1 m/sec and the time between images is 10ms, then it will have traveled 10 mm between successive images. This isapproximately 10% across the field of view. If the sensor is 640H pixelswide, this corresponds to 64 pixels of motion on the image sensor. Yet,for the system 30, using this same example, there would be a movement ofthe object of 20 μm instead of the 10 mm using a conventional globalshutter sensor configuration, and this is equivalent to 0.128 pixelmovement instead of the previously mentioned 64 pixel movement.

For the system 30, since the motion of the object between two images issubstantially less than one pixel, the object is essentially unmovedbetween the two images, and further processing/study/analysis of the twoimages may assume that they were taken simultaneously. Moreover, whendifferent wavelengths of illumination are used, it may be assumed thatany difference between these two images is solely due to the differencein the object (or background) reflectivity in these two wavelengths, andnot due to any motion. It should also be noted that the apparent motionof 0.128 pixels across the sensor 32 is an order of magnitude less thanthe pixel pitch, which may allow for further enhancement andsimplifications in some configurations.

Referring additionally to FIGS. 5 and 6, another global shutter voltagedomain pixel 135 arrangement is shown with dual storage capacitors CST1,CST2 as in the pixel 35, but a single output line Vx. The storagecapacitors CST1, CST2 may still be independently written to using thesignals SAMPLE1 and SAMPLE2, however they share a common output and areboth connected to the line Vx. This has various layout advantages andmay result in a pixel which is smaller and thereby cheaper than theimplementation with two output Vx lines as shown in FIG. 2, and thus maybe desirable in certain applications. However, since there are twostorage elements CST1, CST2 in each pixel 135 but only a single pixeloutput Vx line, the readout is time-division multiplexed.

More particularly, as seen in the timing diagram 145, a result of asingle output terminal with two storage elements CST1, CST2, two pixelreads are used for each row—one for each storage element. Each pixelread cycle typically includes the ADC in each column and its output.Hence the output data is also interleaved between the signals for eachLED.

Under typical usage, the two output signals may be de-interleaved. Thismay be achieved by having an additional digital storage LINE STORE inthe sensor device, as shown in the example system 230 of FIG. 7. Here,the data from the first sample/hold (S/H) readout is converted fromanalog to digital and stored in the digital storage LINE STORE, and thenthe second S/H readout is ADC and readout simultaneously with the datafrom the digital storage LINE STORE. The remaining components 231-237,and 241-243 are similar to their counterparts described above withrespect to FIG. 1. It should be noted that in some implementations, theextra digital storage LINE STORE within the sensor 232 may beundesirable if a small sensor die is required. In such cases, the linestore may be external to the sensor 232.

For certain machine vision applications, a system with only twodifferent wavelengths may be acceptable. However, for otherapplications, e.g., when images are to be viewed by humans, a three (ormore) color system may be used. Turning to FIGS. 8-10, theabove-described approach may be readily extended to operate with three(or more) LEDs L1-L3 (which have respective amplifiers 341, 342, 353) inthe system 330. The remaining components 331-334, 336-337, and 341-343are similar to their counterparts described above with respect to FIG.1.

An example implementation for the pixel 335 for the system 330 is shownin FIG. 9. Note that this configuration further includes additionalswitching transistors T5, T6, as well as source follower transistor SF#4and a third storage capacitor CST3. A voltage domain pixel 335configuration may be desirable due to problems in switching the chargeto different storage elements and the relatively complex processtechnology that this would require. Note that the pixel 335 shown inFIG. 9 has three output bitlines VxA, VxB, VxC. As discussed previously,it is also possible to instead operate with a single bitline which istime-division multiplexed between the three signals, with similarreduction in readout rate.

In the system 330, there is no additional storage (outside of the ADCs244), which restricts the image processing to one dimension (i.e., asingle line). An example type of processing which may be used forcaptured image data is color matrixing as shown in Equation (5) below:

$\begin{matrix}{\begin{pmatrix}Y \\U \\V\end{pmatrix} = {\begin{pmatrix}0.3 & 0.59 & 0.11 \\{- 0.17} & {- 0.33} & 0.50 \\0.50 & {- 0.42} & {- 0.08}\end{pmatrix} \cdot {\begin{pmatrix}R \\G \\B\end{pmatrix}.}}} & (5)\end{matrix}$If 2D image processing of the image is desired, then further storage maybe added. For example, the additional memory may be added between theoutput of the multiplexer X-MUX and the processor 334. The timingdiagram 345 for the system 330 is shown in FIG. 10.

As discussed previously, having three outputs and three ADCs fitting inthe width of each pixel or column may not be feasible in certainimplementations. Hence, in such instances a single output bitline fromeach pixel may be used, along with a single ADC (or other suitablereadout circuitry) and on-chip storage such that all three outputsignals OUT1-OUT3 are available simultaneously. However, it is notnecessary to store the data on-chip, and external line storage orexternal frame storage may also be used.

For certain machine vision applications, a system with four (or more)wavelengths may provide a further advantage. The four wavelengths mayall be in the visible region, or the system may operate with threevisible light sources and one outside the visible spectrum (e.g., NIR700 nm-1000 nm, or NUV 200 nm-400 nm). The above-described systems maybe extended to operate with four (or more) LEDs. Here again, theassociated global shutter pixel may have a corresponding number ofoutput bitlines (i.e., four in this example), or if preferred a singlebitline which is time-division multiplexed between the four signals(with similar reduction in readout rate) may be used, as discussedfurther above. For a four LED configuration, the global shutter sensormay have the ADC pitch ¼ that of the pixel and then have all the ADCsfor a column adjacent, or it may have the ADC pitch ½ that of the pixeland then split the 4 ADCs for each pixel such that two are on top of thearray and two are on the bottom of the array.

Turning now to FIGS. 11 and 12, in the above description, each storageelement in a given global shutter pixel stores a signal whichcorresponds to the charge collected during the illumination phase of thephotodiode. Typically, the photodiode will be buried and can be fullydepleted, and hence there is no reset noise (aka “kTC” noise) on thisnode. However, the floating diffusion (aka “sense node”) capacitor Csnis not fully depleted and it is not possible to reset this nodeperfectly, and so an uncertainty, or noise (reset noise/kTC noise) isgenerated. Typically this node is of small capacitance (1 pF) toincrease the conversion gain of the pixel, and so the voltage noisegenerated on this node {V=SQRT(kT/C)}will be SQRT(1.38E−23*300/1E−15)=2mV. If the full-range swing on the pixel is 1V and is measured with a 10bit ADC, then 2 mV will produce a noise of 2 bits.

In the illustrated example, the pixel 435 and four storage elementsCST1-CST4 in each pixel 435 for use with two sets of LEDs, which makesit possible to compensate for the reset noise using a technique called“correlated double sampling”. With this technique, the sense node(capacitor Csn) is reset, sampled and stored and then thephoto-generated charge is transferred and stored. The difference betweenthese two samples is then free of the reset noise. These operations arerepeated for the second illumination source, and so signals from bothillumination sources are free from reset noise. The pixel 435illustratively includes switching transistors T1-T8.

As seen in the timing diagram 445, at the start of each frame period,signal RST_GS and TG_GS go high, which resets all of the photodiodes PDin all the pixels 435. After these signals go low, then the photodiodeis integrating and the LED L1 is pulsed on. At the end of the LEDillumination phase, the signal RST_GS goes high (but the signal TG_GS iskept low so the photo-generated charge remains on the photodiode), andthe signal SAMPLE1 goes high which causes the reset signal to be sampledon capacitor CST1. The signal RST_GS signal should go low before thesignal SAMPLE1, as it is when the RST_GS signal goes low that the noiseon the floating diffusion is sampled onto the CSN capacitance. Then, thesignal TG_GS goes high, which transfers photo-generated charge stored onthe photodiode to the sense node capacitor Csn, and the signal SAMPLE2signal goes high so that this signal is stored on the capacitor CST2.

This cycle is repeated with LED L2 pulsed on, signal SAMPLE3 causing thereset signal to be stored on the capacitor CST3, and the signal SAMPLE4causing the photo-signal to be stored on the capacitor CST4. Note thatin this approach, the signals stored in the pixels 435 are not read outof the pixel array until after the signal SAMPLE4 occurs, which allowsfor a very rapid operation between the pulsing of the LEDs, e.g., 1 μsto 10 μs.

The signals may be read out in a row-by-row fashion. If there are fouroutputs conductors per pixel, then a correction may be provided for thevariation in threshold voltages of the source follower's in each pixel.There are various ways to achieve this, one of which is to readout thestored values on capacitors CST1-CST4, then turn on the signal RST_GSand read out a reference voltage to compensate the variation inthreshold voltages.

Another embodiment of the noise reduction configuration described aboveis now described with reference to FIGS. 13 and 14. In the illustratedglobal shutter pixel 535, the capacitor CST1 stores the reset signalfrom the first LED exposure (VDD−VKTC1), the capacitor CST2 stores theexposed signal from the first exposure (VDD−VKTC1−Vphoto1), thecapacitor CST3 stores the reset signal from the second LED exposure(VDD−VKTC2), and the capacitor CST4 stores the exposed signal from thesecond LED exposure (VDD−VKTC2-Vphoto2). Moreover, voltages VTS1 andVTS2 are the threshold voltages on the two output source followertransistors SF#2, SF#3.

Since there are four voltages stored on capacitors CST1-CST4(VCST1−VCST4, respectively) and two output conductors VxF and VxS, tworead operations are used to read them out, as follows

Phase 1:

Take READ13 high and READ24 low

VxF₁ is VCST1−VTS1, and

VxS₁ is VCST3−VTS2.

(Note that the “1” subscript indicates that this is the voltage on thefirst phase of reading).

Phase 2:

Take READ13 low and READ24 high

VxF₂ is VCST2−VTS1, and

VxS₂ is VCST4−VTS2.

Now subtracting these pairs of signals:VCDS1=VxF ₂ −VxF ₁=(VCST2−VTS1)−(VCST1−VTS1)=(VCST2−VCST1), andVCDS2=VxS ₂ −VxS ₁=(VCST4−VTS2)−(VCST3−VTS2)=(VCST4−VCST3).Hence the threshold voltages from the output source follower transistorsare cancelled. Further, the kTC noise is cancelled:VCDS1=(VDD−VKTC1)−(VDD VKTC1−Vphoto1)=Vphoto1, andVCDS2=(VDD−VKTC2)−(VDD−VKTC2−Vphoto2)=Vphoto2

Note that in the pixel 535 shown in FIG. 13, there is charge sharingbetween the larger (e.g., 15 fF type) storage capacitor and the smaller(e.g., 1 fF) of the gate of the source follower. Hence the voltage onthe gate OSFG1 or OSFG2 prior to signals READ13 or READ24 going activewill affect the voltage of the gate OSFG1 or OSFG2 after the signalREAD13/READ24 goes active. Hence, it may be desirable to pre-chargethese voltages to a fixed level so that the charge sharing effect isconstant and there is no memory of previous values (VCST1 to VCST4) fromprevious images, which would affect (i.e., add noise) to the readout.This may be achieved by adding the transistors T9, T10 which allow thegate OSFG1 and OSFG2 to be charged to a predefined voltage (VRT in thisexample) prior to the signals READ13 and READ14 going high. It should benoted that the signals READ13, READ24, and PREQOUT, may be global to thesensor (i.e., connected to all the pixels on the array), or be local toa row (i.e., gated with the row select signal, e.g. the signal READ_Rn).

In the foregoing embodiments, the different optical sources (i.e., theLEDS L1, L2, etc.) are co-located and each emits light at differentrespective wavelengths, as discussed above. However, in differentembodiments, the optical sources may be spaced apart and/or of a sameoptical wavelength. By way of example, this approach may be used toprovide depth map imaging or ranging to an object using a “structuredlight” approach. In this regard, a pattern of light (e.g., such asstripes, dots, or a pseudo-random pattern)—which may be visible orinvisible to the human eye, such as near infrared—is projected onto ascene. Using parallax, the distortion of this pattern may be observedand the depth may be deduced.

Using two (or more) sources of light which are spaced apart allows fortwo different measurements, and a distance may accordingly be calculatedfrom these measurements. In accordance with an example global shutterimplementation, the optical sources may be at least 5 cm apart, althoughother distances may be used in different configurations. Here again,optical data from the different optical sources is stored in respectivestorage capacitors during each of the integration periods before anyread out, which advantageously provides for relatively little timebetween the image captures to avoid any significant degradation inaccuracy of the distance measurement due to movement of the object (orsensor) during the reading phase, as described further above.

A related optical imaging method is now described with reference to theflow diagram 600 of FIG. 15. Beginning at Block 601, the methodillustratively includes causing a first optical source L1 (see FIG. 1)from among a plurality of optical sources L1-L2 to illuminate a firstone of storage elements CST1 in each global shutter pixel 35 to storeoptical data during a first integration period, at Block 602. The methodmay further include causing a second one of the optical sources L2 toilluminate a second one of the storage elements CST2 in each globalshutter pixel 35 to store optical data during a second integrationperiod, at Block 603. As noted above, the optical sources L1, L2 may beof the same or different wavelengths, and they may be co-located orspaced apart. The method further illustratively includes outputting thestored optical data from the first and second storage elements of theglobal shutter pixels after the first and second integration periods, atBlock 604, which illustratively concludes the method of FIG. 15 (Block605).

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. An optical electronic device comprising: aplurality of different optical sources; a global shutter sensorcomprising an array of global shutter pixels, each global shutter pixelcomprising a plurality of amplifiers and a plurality of storage elementscoupled to one or more inputs of the plurality of amplifiers; and acontroller coupled to said plurality of optical sources and said globalshutter sensor and configured to cause a first one of the opticalsources to illuminate and a first one of the storage elements in eachglobal shutter pixel to store optical data during a first integrationperiod, cause a second one of the optical sources to illuminate and asecond one of the storage elements in each global shutter pixel to storeoptical data during a second integration period, cause an input of afirst one of the amplifiers to charge to a predefined voltage prior toan outputting of the stored optical data from the first storage element,cause an input of a second one of the amplifiers to charge to thepredefined voltage prior to an outputting of the stored optical datafrom the second storage element, and output the stored optical data fromthe first and second storage elements of said global shutter pixelsafter the first and second integration periods.
 2. The opticalelectronic device of claim 1 wherein said plurality of optical sourcesare spaced apart from one another.
 3. The optical electronic device ofclaim 1 wherein the plurality of different optical sources comprises anon-visible light source, and wherein the non-visible light source has awavelength in a range of 200 nm to 400 nm.
 4. The optical electronicdevice of claim 1 wherein the plurality of different optical sourcescomprises a visible light source, and wherein the visible light sourcehas a wavelength in a range of 400 nm to 700 nm.
 5. The opticalelectronic device of claim 1 wherein the plurality of different opticalsources comprises a non-visible light source, and wherein thenon-visible light source has a wavelength in a range of 700 nm to 1000nm.
 6. The optical electronic device of claim 1 wherein said globalshutter sensor further comprises a plurality of analog-to-digitalconverters (ADCs) coupled to said array of global shutter pixels; andwherein said controller reads the stored optical data by causing theADCs to convert the optical data to digital optical data.
 7. The opticalelectronic device of claim 6 wherein said global shutter sensor furthercomprises a multiplexer coupled to said ADCs configured to multiplex thedigital optical data from said ADCs as an output of said global shuttersensor.
 8. The optical electronic device of claim 6 wherein said globalshutter pixels are arranged in rows and columns in said array; whereineach column of said array comprises a plurality of bit lines; andwherein said plurality of ADCs comprises a respective ADC for each ofthe bit lines.
 9. The optical electronic device of claim 1 wherein thestorage elements comprise capacitors.
 10. The optical electronic deviceof claim 1 wherein said controller is further configured to cause athird one of the optical sources to illuminate and a third one of thestorage elements in each global shutter pixel to store optical dataduring a third integration period, and to output the stored optical datafrom the first, second, and third storage elements of said globalshutter pixels after the first, second, and third integration periods.11. The optical electronic device of claim 1 wherein said controller isfurther configured to cause third and fourth storage elements from amongthe plurality of storage elements to respectively store reset signalsassociated with the first and second integration periods; and whereinsaid controller is further configured to remove respective reset noisefrom the optical data stored in the first and second storage elementsbased upon the reset signals stored in the third and fourth storageelements.
 12. An image sensor for use with a plurality of differentoptical sources, the image sensor comprising: a global shutter sensorcomprising an array of global shutter pixels, each global shutter pixelcomprising a plurality of storage elements and a plurality of sourcefollowers having gate terminals coupled to the plurality of storageelements; and a controller coupled to said plurality of optical sourcesand said global shutter sensor and configured to cause a first one ofthe optical sources to illuminate and a first one of the storageelements in each global shutter pixel to store optical data during afirst integration period, cause a second one of the optical sources toilluminate and a second one of the storage elements in each globalshutter pixel to store optical data during a second integration period,cause a gate terminal of a first one of the plurality of sourcefollowers to charge to a fixed voltage after the first integrationperiod and prior to an outputting of the stored optical data in thefirst storage element, cause a gate terminal of a second one of theplurality of source followers to charge to the fixed voltage after thesecond integration period and prior to an outputting of the storedoptical data in the second storage element, and output the storedoptical data from the first and second storage elements of said globalshutter pixels after the first and second integration periods.
 13. Theimage sensor of claim 12 wherein said plurality of optical sources arespaced apart from one another.
 14. The image sensor of claim 12 whereinsaid global shutter sensor further comprises a plurality ofanalog-to-digital converters (ADCs) coupled to said array of globalshutter pixels; and wherein said controller reads the stored opticaldata by causing the ADCs to convert the optical data to digital opticaldata.
 15. The image sensor of claim 14 wherein said global shuttersensor further comprises a multiplexer coupled to said ADCs configuredto multiplex the digital optical data from said ADCs as an output ofsaid global shutter sensor.
 16. The image sensor of claim 14 whereinsaid global shutter pixels are arranged in rows and columns in saidarray; wherein each column of said array comprises a plurality of bitlines; and wherein said plurality of ADCs comprises a respective ADC foreach of the bit lines.
 17. An optical imaging method for a globalshutter sensor comprising an array of global shutter pixels, each globalshutter pixel comprising a plurality of storage elements and a pluralityof amplifiers having inputs coupled to at least one of the plurality ofstorage elements, the method comprising: causing a first optical sourcefrom among a plurality of different optical sources to illuminate and afirst one of the storage elements in each global shutter pixel to storeoptical data during a first integration period; causing a second one ofthe optical sources to illuminate and a second one of the storageelements in each global shutter pixel to store optical data during asecond integration period; causing an input of a first one of theplurality of amplifiers to charge to a predetermined voltage after thefirst integration period and the second integration period; causing aninput of a second one of the plurality of amplifiers to charge to thepredetermined voltage after the first integration period and the secondintegration period; and outputting the stored optical data from thefirst and second storage elements of the global shutter pixels after thefirst and second integration periods.
 18. The method of claim 17 whereinthe plurality of optical sources are spaced apart from one another. 19.The method of claim 17 wherein the global shutter sensor furthercomprises a plurality of analog-to-digital converters (ADCs) coupled tothe array of global shutter pixels; and wherein outputting comprisesreading the stored optical data by causing the ADCs to convert theoptical data to digital optical data.
 20. The method of claim 17 furthercomprising causing a third one of the optical sources to illuminate anda third one of the storage elements in each global shutter pixel tostore optical data during a third integration period; and whereinoutputting comprises outputting the stored optical data from the first,second, and third storage elements of the global shutter pixels afterthe first, second, and third integration periods.
 21. The method ofclaim 17 further comprising: causing third and fourth storage elementsfrom among the plurality of storage elements to respectively store resetsignals associated with the first and second integration periods; andremoving respective reset noise from the optical data stored in thefirst and second storage elements based upon the reset signals stored inthe third and fourth storage elements.